DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2017-0814; Product Identifier 2017-NM-066-AD; Amendment
39-19458; AD 2018-20-24]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: We are adopting a new airworthiness directive (AD) for certain
The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER
series airplanes. This AD was prompted by significant changes made to
the airworthiness limitations (AWL) related to fuel tank ignition
prevention and the nitrogen generation system. This AD requires
revision of the maintenance or inspection program, as applicable, to
include the latest revision of the AWLs. We are issuing this AD to
address the unsafe condition on these products.

DATES: This AD is effective November 19, 2018.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of November 19,
2018.

ADDRESSES: For service information identified in this final rule,
contact Boeing Commercial Airplanes, Attention: Contractual & Data
Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA
90740-5600; telephone 562-797-1717; internet https://www.myboeingfleet.com.
You may view this service information at the
FAA, Transport Standards Branch, 2200 South 216th St., Des Moines, WA.
For information on the availability of this material at the FAA, call
206-231-3195. It is also available on the internet at http://www.regulations.gov
by searching for and locating Docket No. FAA-2017-0814.

Examining the AD Docket

You may examine the AD docket on the internet at http://www.regulations.gov
by searching for and locating Docket No. FAA-2017-
0814; or in person at Docket Operations between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays. The AD docket contains
this final rule, the regulatory evaluation, any comments received, and
other information. The address for Docket Operations (phone: 800-647-
5527) is Docket Operations, U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Tak Kobayashi, Aerospace Engineer,
Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3553; email:
takahisa.kobayashi@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR
part 39 by adding an AD that would apply to certain The Boeing Company
Model 737-600, -700, -700C, -800, and -900 series airplanes. The NPRM
published in the Federal Register on October 2, 2017 (82 FR 45743). The
NPRM was prompted by significant changes made to the AWLs related to
fuel tank ignition prevention and the nitrogen generation system. The
NPRM proposed to require revision of the maintenance or inspection
program, as applicable, to include the latest revision of the AWLs.
In the NPRM, we discussed that we would mandate the latest revision
of the Airworthiness Limitations section (ALS) of the Instructions for
Continued Airworthiness (ICA) as of the effective date of the AD for
Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes
with an original certificate of airworthiness or original export
certificate of airworthiness that was issued on or before the effective
date of the AD. We also discussed that operators of airplanes with an
original certificate of airworthiness or original export of certificate
of airworthiness issued after the effective date of the AD must comply
with the ALS revision specified as part of the approved type design.
Since the issuance of the NPRM, Boeing revised the ALS a number of
times and added new AWL tasks. In order to mandate the latest ALS
revision available as of the effective date of the AD as we originally
proposed, we must supplement the NPRM for public comments because new
additional AWL tasks in the later ALS revisions expand the scope of the
NPRM. As a result, the issuance of the AD to address the unsafe
condition would be delayed.
Based on those conditions, we have made the following adjustments
in this final rule. First, instead of mandating the latest ALS
revision, we are mandating Revision January 2017 of the ALS as
originally proposed in the NPRM. Second, we have changed the AD
applicability to exclude those airplanes delivered with later ALS
revisions (later than Revision January 2017) as part of the type
design. The change in the AD applicability is intended to avoid the
situation discussed in the NPRM where the AD mandates a specific ALS
revision for an airplane that was delivered with a later ALS revision
as part of the type design. Airplanes outside the AD applicability
should use the ALS revision later than Revision January 2017 as part of
the type design. Those adjustments we made in the final rule do not
expand the scope of the NPRM. We will consider further rulemaking to
mandate a later ALS revision for all affected airplanes.
We are issuing this AD to address the development of an ignition
source inside the fuel tanks and the flammability exposure of the
center fuel tank, which could lead to fuel tank explosion and
consequent loss of the airplane. We are also issuing this AD to address
the loss of engine fuel suction feed capability, which could result in
dual engine flameout, inability to restart engines, and consequent
forced landing of the airplane.

Comments

We gave the public the opportunity to participate in developing
this final rule. The following presents the comments received on the
NPRM and the FAA's response to each comment.

Support for the NPRM

Commenter Nick Gianetti supported the NPRM.

Request To Clarify the Provision for Exceptional Short-Term Extensions

Southwest Airlines requested clarification regarding the provision
for ``exceptional short-term extension'' in the service information.
We agree that clarification is necessary. Operators may use an
exceptional short-term extension with the concurrence of the
appropriate authority, as described in the service information.
Exceptional short-term extensions should be used to address
uncontrollable or unexpected situations. For any change to the interval
of an AWL other than an exceptional short-term extension, approval must
be handled under the provisions of paragraph (k) of this AD. No change
to this AD is necessary.

Request To Identify AD 2011-20-07, Amendment 39-16818 (76 FR 60710,
September 30, 2011) (``AD 2011-20-07''), as an Affected AD

Boeing stated that AD 2011-20-07 is affected by the proposed AD
because it relates to an AWL in the mandated service information. They
requested that we identify AD 2011-20-07 as an affected AD under
paragraph (b) of the proposed AD.
We acknowledge the commenter's rationale for including AD 2011-20-
07 in paragraph (b) of this AD. However, paragraph (b), ``Affected
ADs,'' is intended to include other affected ADs, but not all related
ADs. It is primarily used to reference superseded ADs and other ADs
that are terminated, in whole or in part, by requirements in a given
AD. Although compliance with certain requirements in AD 2011-20-07
affects this AD, the opposite is not true (i.e., this AD does not
affect compliance with AD 2011-20-07). Therefore, we have not changed
this AD regarding this issue.

Request To Specify the Unsafe Condition for Engine Fuel Suction Feed

Boeing stated that the NPRM defines the unsafe condition for fuel
tank ignition prevention and fuel tank flammability exposure reduction,
but not the unsafe condition related to engine fuel suction feed.
Because the proposed AD also requires the incorporation of the AWL for
engine fuel suction feed testing, Boeing asserted that the unsafe
condition associated with engine fuel suction feed should also be
specified, and they proposed wording for the unsafe condition.
We partially agree with the commenter. We agree to specify the
unsafe condition associated with engine fuel suction feed, but we
disagree with the wording proposed by the commenter because this AD
does not mandate repetitive operational tests of the engine fuel
suction feed system. This AD requires only the incorporation of certain
AWLs, not the repetitive operational tests or other procedures
specified in them. We have changed paragraph (e) of this AD to include
the unsafe condition involving engine fuel suction feed.

Request To Change Wording in the Proposed AD

Boeing requested that we replace the word ``latest'' with ``later''
in certain subparagraphs of paragraph (g) of the proposed AD in which
multiple compliance times are compared.
We do not agree with the commenter's request because the
subparagraphs in question compare three compliance times; therefore,
the superlative form ``latest'' is correct. We have not changed this AD
in this regard.

Request To Provide a Grace Period in Paragraph (g)(7) of the Proposed
AD

Southwest Airlines stated that some airplanes could be out of
compliance as of the effective date of the proposed AD because the
initial 120-month compliance time specified in paragraph (g)(7) of the
proposed AD may already have passed for those airplanes. Southwest
Airlines requested that we change paragraph (g)(7) of the proposed AD
to specify a grace period.
We agree to specify a grace period for those airplanes that could
have passed the required compliance time specified in paragraph (g)(7)
of this AD. Therefore, we have changed paragraph (g)(7) of this AD to
specify a grace period of 24 months after the effective date of this
AD.

Request To Delete Paragraph (h) of the Proposed AD

Boeing stated that some of the wire types listed in paragraph
(h)(1) of the proposed AD are not identified in FAA Advisory Circular
43-13-1B for the flammability aspect. Boeing also stated that they do
not have arc-track test data for the wires listed in paragraph (h)(1)
and therefore cannot accept the use and installation of these wire
types on a Boeing product without written FAA approval of the wires. In
addition, Boeing stated that it has data for TFE-2X Standard wall, but
not for Roundit 2000NX and Varglas Types HO, HP, or HM and can
therefore approve or recommend approval of only the TFE-2X Standard
wall. Boeing requested that we delete paragraph (h) of the proposed AD
or revise it to include an FAA-issued global alternative method of
compliance (AMOC) that identifies the material listed in paragraph (h)
of the proposed AD. Boeing stated that if the FAA decides to keep
paragraph (h) of the proposed AD as it is, we should state that all
materials listed in paragraph (h) of the proposed AD are approved by
the FAA.
We do not agree with the commenter's request. Paragraph (h) of this
AD allows alternative wire types and sleeving materials for certain
wire types and sleeving materials identified in AWL No. 28-AWL-05. AWL
No. 28-AWL-05 was originally mandated by AD 2008-10-10, Amendment 39-
15516 (73 FR 25986, May 8, 2008) (``AD 2008-10-10''), which was later
revised to AD 2008-10-10 R1, Amendment 39-16164 (75 FR 1529, January
12, 2010) (``AD 2008-10-10 R1''). Since the issuance of AD 2008-10-10
R1, which will be terminated by this AD, we have received numerous
requests for approval of AMOCs from operators and supplemental type
certificate (STC) holders (or applicants) to allow the installation of
alternative wire types and sleeving. We evaluated certain attributes of
those alternative wire types and sleeving for each installation, and
issued numerous AMOC approvals for AD 2008-10-10 R1 based on our
determination that the installation of those wire types and sleeving
would provide an acceptable level of safety. The alternative wire types
and sleeving specified in paragraph (h) of this AD were previously
approved as an AMOC for AD 2008-10-10 R1. Although paragraph (h) of
this AD provides certain allowances, it does not provide approval of
alternative wire types and sleeving that are installed as part of an
aircraft design change. Each applicant for any design change is
responsible to show that the installation of alternative wire types and
sleeving identified in paragraphs (h)(l) and (h)(2) of this AD complies
with all applicable regulatory requirements, including flammability
requirements, as the commenter pointed out. We have not changed this AD
in this regard.

Request To Specify Additional Wire Type Specifications in Paragraph
(h)(1) of the Proposed AD

Delta Airlines (DAL) stated that the military wire specifications
identified in paragraph (h)(1) of the proposed AD have been superseded.
DAL requested that we revise paragraph (h)(1) of the proposed AD to
identify additional wire type specifications.
We agree with the commenter and have revised paragraph (h)(l) of
this AD to identify additional acceptable SAE and military wire type
specifications.

Request To Specify Sleeving Thickness

Boeing stated that under AWL No. 28-AWL-05, the wall thickness
requirement for TFE-2X sleeving is specified as ``standard wall.''
Boeing requested that we also specify the wall thickness requirement
for Varglas Type HO, HP, and HM, that are allowed as alternative
sleeving under paragraph (h)(2) of the proposed AD.
We do not agree with the commenter's request. As we explained in an
earlier comment response, paragraph (h)(2) of this AD provides certain
allowances for sleeving material to comply with AWL No. 28-AWL-05, but
it does not provide approval of alternative sleeving that is installed
as part of an aircraft design change. Each applicant for any design
change is responsible to show that the installation of alternative
sleeving identified in paragraph (h)(2) of this AD complies with all
applicable regulatory requirements. This includes substantiation to
show that sleeve installation, including the selection of sleeve
thickness, is adequate to protect wires from chafing for the life of
installation. We have not changed this AD regarding this issue.

Request To Mandate a Later Revision of the Service Information

Boeing stated that Boeing 737-600/700/700C/800/900/900ER Special
Compliance Items/Airworthiness Limitations, D626A001-9-04, Revision
January 2017, specified by the proposed AD, is under review and subject
to update. Boeing requested that we mandate a later revision of the
service information.
We do not agree with the commenter's request. As stated in the
Discussion section of this AD, we have determined that it is
appropriate to require the same ALS revision (Revision January 2017)
that was proposed in the NPRM. We have also adjusted the applicability
of this AD to exclude those airplanes delivered with a later ALS
revision (issued after Revision January 2017) as part of the type
design.

Effect of Winglets on Accomplishment of the Proposed Actions

Aviation Partners Boeing stated that accomplishing the STC
ST00830SE does not affect the actions specified in the proposed AD.
We concur with the commenter that STC ST00830SE does not affect the
accomplishment of the manufacturer's service instructions. Therefore,
the installation of STC ST00830SE does not affect the ability to
accomplish the actions required by this AD. We have not changed this AD
in this regard.

Conclusion

We reviewed the relevant data, considered the comments received,
and determined that air safety and the public interest require adopting
this final rule with the changes described previously and minor
editorial changes. We have determined that these minor changes:
Are consistent with the intent that was proposed in the
NPRM for addressing the unsafe condition; and
Do not add any additional burden upon the public than was
already proposed in the NPRM.
We also determined that these changes will not increase the
economic burden on any operator or increase the scope of this final
rule.

Related Service Information Under 1 CFR Part 51

We reviewed Boeing 737-600/700/700C/800/900/900ER Special
Compliance Items/Airworthiness Limitations, D626A001-9-04, Revision
January 2017. This service information describes AWLs that include
airworthiness limitation instructions (ALI) and critical design
configuration control limitations (CDCCL) tasks related to fuel tank
ignition prevention and the nitrogen generation system. This service
information is reasonably available because the interested parties have
access to it through their normal course of business or by the means
identified in the ADDRESSES section.

Costs of Compliance

We estimate that this AD affects 1,850 airplanes of U.S. registry.
We estimate the following costs to comply with this AD:
We have determined that revising the maintenance or inspection
program takes an average of 90 work-hours per operator, although we
recognize that this number may vary from operator to operator. In the
past, we have estimated that this action takes 1 work-hour per
airplane. Since operators incorporate maintenance or inspection program
changes for their affected fleet(s), we have determined that a per-
operator estimate is more accurate than a per-airplane estimate.
Therefore, we estimate the total cost per operator to be $7,650 (90
work-hours x $85 per work-hour).

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, section 106, describes the
authority of the FAA Administrator. Subtitle VII: Aviation Programs,
describes in more detail the scope of the Agency's authority.
We are issuing this rulemaking under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701: ``General
requirements.'' Under that section, Congress charges the FAA with
promoting safe flight of civil aircraft in air commerce by prescribing
regulations for practices, methods, and procedures the Administrator
finds necessary for safety in air commerce. This regulation is within
the scope of that authority because it addresses an unsafe condition
that is likely to exist or develop on products identified in this
rulemaking action.
This AD is issued in accordance with authority delegated by the
Executive Director, Aircraft Certification Service, as authorized by
FAA Order 8000.51C. In accordance with that order, issuance of ADs is
normally a function of the Compliance and Airworthiness Division, but
during this transition period, the Executive Director has delegated the
authority to issue ADs applicable to transport category airplanes and
associated appliances to the Director of the System Oversight Division.

Regulatory Findings

This AD will not have federalism implications under Executive Order
13132. This AD will not have a substantial direct effect on the States,
on the relationship between the national government and the States, or
on the distribution of power and responsibilities among the various
levels of government.
For the reasons discussed above, I certify that this AD:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Is not a ``significant rule'' under DOT Regulatory Policies and
Procedures (44 FR 11034, February 26, 1979),
(3) Will not affect intrastate aviation in Alaska, and
(4) Will not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.

Adoption of the Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. The FAA amends Sec. 39.13 by adding the following new airworthiness
directive (AD):